Aftertreatment devices are well known and used for the aftertreatment of engine exhaust gases and materials in, for example, various internal combustion engine applications such as heavy duty diesel engines. Closed coupled catalysts, for example, are useful for handling and/or removing exhaust materials including carbon monoxide, unburned hydrocarbons, and soot present in the exhaust stream of an engine, and are useful for converting nitric oxide to nitrogen dioxide to enable passive regeneration of a diesel particulate filter or to enhance conversion in selective catalytic reduction systems.
In the example of closed coupled catalysts, current formation techniques include rolling a metal shell over a catalyst substrate. Joining a metallic closed coupled catalyst to the greater exhaust system also rely on formation of mechanical couplings such as flanges or weldments. Such techniques, however, can require extensive tooling which is proved to be less cost effective. For example, in addition to formation of the shell and catalyst substrate, current designs also need a plurality of components such as welded end cones to connect to the main shell and catalyst substrate, in order to satisfy multiple junctions. The resulting catalyst is overall costly and complicated to produce.
Due to original equipment manufacturer space constraints, the need to package catalyst substrates in smaller and sometimes unique spaces is increasing. Catalyst devices, for example closed coupled catalysts, are being produced that are not always in the shape of a conventional circle. For example, other elliptical and other odd shapes that are not the shape of a circle are often desired.
As an alternative to the current rolling and joining techniques, spin formed metallic packages have been contemplated as another approach to manufacturing aftertreatment devices. In general, spin forming is known as a very flexible manufacturing method that minimizes tooling expense versus other traditional methods. Spin forming techniques typically employ discs or tubes of metal that are rotated at high speeds and are cold formed (i.e. at ambient temperature) into a die to shape an outside diameter or onto a mandrel to shape an inside diameter. Spin forming has been known to be useful in generally forming circle shaped components, but has not been suitably developed in the area of catalyst formation.
Unfortunately, current attempts to produce aftertreatment devices using spin forming techniques form the shell directly to the catalyst substrate. This formation technique results in, for example metal to metal contact between the shell and the mantle of the catalyst substrate, or perhaps metal to ceramic contact between the shell and the substrate. Such direct contact between the shell and the catalyst substrate can have a propensity to vibrate during extended operation either creating acute noise, vibration, and harshness (NVH) issues, or resulting in chronic failure of the overall device due to mechanical fatigue. Further, a viable joint between the inside of the shell and the outside of the catalyst substrate cannot consistently be achieved. As a result, leakage of exhaust gas and blowby around or past the catalyst substrate without being treated can lead to degradation of emissions performance. In examples where a ceramic catalyst substrate is employed, the use of spin forming the shell and the catalyst substrate in direct contact can also cause cracking of the catalyst substrate and render it unworkable. Catalyst washcoat spalling and loss of catalyst chemical performance can present further problems in such designs. These drawbacks are of particular concern for catalyst devices that are of an elliptical or other odd shape and that are not the shape of a circle. Where OEMs require catalyst devices with geometry that cannot be defined by a single parameter such as a radius, such current attempts are not practicable.
Ceramic mats have been used to seal various catalyst substrates in for example a diesel oxidation catalyst (DOC), diesel particulate filter (DPF), selective catalytic reduction (SCR) systems, NOx adsorber catalyst (NAC), partial filter and urea hydrolysis catalyst (UHC), and precious metals catalysts. These catalysts, however, do not undergo a spin forming process. Rather, these rigid elements are captured by sizing the compliant mat with the rigid aftertreatment shell to achieve appropriate gap bulk density (GBD) targets required for element retention.
Despite existing technology, there remains a challenge to bring to production and to improve upon catalyst devices such as closed coupled catalysts, in terms of acceptable reliability and durability, and while capably taking advantage of spin forming production techniques.